Numerous types of touch-controlled electronic switches are available. They are generally reliable and safe but contain one or more drawbacks that are overcome by the present invention. For instance, T. Kohler, U.S. Pat. No. 4,250,432 on "Touch Dimmer Circuit" issued Feb. 10, 1981 is exemplary of the touch-controlled dimmer approach which utilizes a thyristor to control power to a load where the thyristor is selectively gated on by an integrated circuit responsive to a capacitive sensitive circuit or touch sensor. Such devices are incapable of providing discrete, repeatable power level stepping and are subject to over control which requires an operator to completely recycle the system in an attempt to achieve a desired level.
Wern in U.S. Pat. Nos. 3,811,054; 4,210,822; and 4,289,972 discloses a typical touch-responsive switching system for lighting installations relying on alternating current as a power source. Systems such as these require synchronization between the alternating current power source and switching control signals. To achieve the required synchronization, such devices bridge the alternating current supply and since they include relatively sensitive digital control circuitry, they are subject to damage in the event of current spikes which are common on supply lines.
Isaacs, U.S. Pat. No. 3,766,431 on "Lighting Control System Including An Analog-To-Digital Converter", which uses a digital store to control the brightness of a lamp, and G. Kappenhagen, U.S. Pat. No 3,874,460 on "Synthesis Of Dimmer Output Revisor Within The Dimmer Logic Circuit" are further examples of the use of overly complex and expensive circuitry to control current to an appliance.
T. Bobick, U.S. Pat. No. 4,103,252 "Capacitive Touch-Activated Transducer System Including A Plurality Of Oscillators" requires a plurality of oscillators and special geometry of the electrodes on the touch plate, all of which increase cost and reduce reliability.
W. Hamilton II, U.S. Pat. No. 4,081,700 on "Touch Control Switch Circuit With Compensation For Power Supply Line Fluctuations" teaches still another touch responsive means for controlling alternating current. In this system the alternating current induces a hum signal in a human body near the supply line. A touch receptor provides a hum signal which changes in amplitude when it picks up the additional hum signal from a human body touching the detector and this increase in amplitude is interpreted as a power supply control signal. Systems such as this are extremely delicate and subject to variations in performance resulting from differing electrical characteristics of different human bodies and cannot provide precise stepped intensity control.
R. Sherman, U.S. Pat. No. 4,287,468 on "Dimmer Control System" is representative of systems which utilize a digital memory to store predetermined bit sequences which represent different levels of power. A data signal representing the desired level of power is generated and synchronized with zero crossing of the voltage waveform of the power source being controlled. The resultant signal represents an address of the memory device storing the predetermined bit sequences and through this technique, the addressed memory device supplies a control input to a means for gating on a triac for a predetermined period of time during a power half cycle. Devices such as these are fairly complex and generally not responsive to touch control inputs.
N. Instance, U.S Pat. No. 4,237,386 on "Plug-In Module For Touch Control Switching" is exemplary of plug in modules for remote, touch responsive switching means. Such systems are similar to that presented by this patent but limited and more costly to produce because they require a specifically designed power plug for the appliance in combination with a control module that must be plugged into the specially designed appliance plug. In the present invention, control is provided by a single module which may be plugged into any standard AC outlet and to which any appliance utilizing a standard AC plug may be connected.
The fact that such a large number of different approaches to lamp control exists, as exemplified by the preceding examples, suggests that heretofore a satisfactory touch-responsive control has not been available.